Transmission path switching is an essential function in transmission paths of optical signals. For example, optical fiber systems typically comprise the following: an optical switching function for switching the path to a new one to select an optical signal from a plurality of transmission paths, an optical monitoring function for monitoring a status of each path, etc. To this end, a mechanical optical switch for switching the optical path by relatively moving end surfaces of optical fibers facing each other is simple in structure and has desirable features such as low insertion loss, miniaturization, etc. A lot of configurations have been proposed for this type mechanical optical switch.
For example, Japanese Patent Publication No. H11-295623A has disclosed a pressing mechanism for pressing optical fiber end surfaces against each other in order to suppress loss, after a photodetecting side optical fiber is moved and positioned along arrangement of a plurality of transmission side optical fibers. Both movement and pressing are carried out by an ultrasonic linear motor and a stop position of the photodetecting side optical fiber is controlled by a computer.
Further, as described in Japanese Patent Publication No. H07-72398A, there is a known method in which optical fibers are fixed into V-grooves (grooves each shaped like a V figure in section) to thereby improve positional accuracy after switching. In the condition that the plurality of optical fibers are fixed into the V-grooves, an optical fiber facing the plurality of optical fibers is moved among the V-grooves by a drive mechanism to thereby switch the optical path.
Further, as described in Japanese Patent Publication No. H08-50253A, there has been proposed an optical switch in which a plurality of optical fibers are arranged on a surface of a column and the column is rotated by a stepping motor to thereby couple one of the optical fibers to an optical fiber facing the optical fibers.
In the mechanical optical switch for distributing signals from a plurality of optical fibers, it is necessary to optically couple a transmission side optical fiber and a reception side optical fiber to each other with a low coupling loss. That is, a mechanism for making optical axes of the transmission and reception side optical fibers coincident with each other after a switching operation is required. In order to make the optical axes coincident with each other highly accurately, a fixing jig having a V-groove structure as described above, an alignment marker, or the like, is generally used. Since these are used in combination with a drive mechanism for performing mechanical movement, there is a problem that the apparatus is complicated in structure. When the structure is complicated, there is another problem that characteristic is apt to vary on a long-term basis due to environmental change, etc. For this reason, a special mechanism for pressing optical fiber end surfaces, etc. may be additionally required to result in a further complicated structure.
In an optical switch having the V-groove structure, switching at a high speed is not easy because each optical fiber has to be once floated from a corresponding V-groove and moved when switching is performed. An operation of pressing end surfaces against each other after the movement is not adapted for high-speed switching.
In consideration of the foregoing problems, an object of the invention is to provide an optical path switching apparatus such as an optical switch or an optical monitor and an optical path switching method, each of which is simple in structure, capable of performing switching at a high speed and stable in characteristic against environmental change.
(2) An optical fiber is widely used as an optical signal transmission path for connecting a light source for converting an electric signal into an optical signal and a photo detector for converting the optical signal to an electric signal to each other. A large number of such transmission paths are arranged with increase in the volume of transmission information, so that a path from a light source to a photo detector is complicated. In order to maintain the complicated transmission paths stable over a long term, an optical monitor for monitoring occurrence of failure in anyone of the transmission paths is required.
In the optical monitor for optical transmission paths, there is adopted a means for splitting an optical fiber for inspection basically in the middle of each transmission path and detecting an inspection signal by a photo detector. For example, in a system disclosed in Japanese Patent Publication No. H06-58840A, a transmission path to be inspected is selected from a plurality of active transmission paths by an optical switch, an optical coupler is used to couple and inject an inspection signal different in wavelength from a transmission signal into the transmission path, a signal light reflected from a terminal end of the transmission path is detected by a photo detector, and the output thereof is monitored.
As represented by the aforementioned example, a conventional optical monitor on the optical fiber transmission paths has a means for coupling each optical fiber and an inspection signal to each other with high coupling efficiency. In order to monitor a large number of transmission paths, it is however necessary to provide an optical coupling system for each path and dispose a photo detector to monitor the output thereof, or it is however necessary to use a means for switching optical coupling as described in the aforementioned example. In the former case, there is a problem that the number of components for constituting the optical monitor increases and a signal processing system for monitoring the transmission paths as a whole is complicated. Further, in the latter case, there is another problem that optical coupling has to be maintained whenever the optical path is switched and that a long time is required for inspection when the number of paths is large.
Another object of the invention is to provide an optical monitor that can monitor a large number of transmission paths at a high speed in spite of a small number of components.